code: def bfs_predecessors(
      G, source, depth_limit=None, sort_neighbors=None
  ):
      """Returns an iterator of predecessors in breadth-first-search from source.
  
      Parameters
      ----------
      G : NetworkX graph
  
      source : node
         Specify starting node for breadth-first search
  
      depth_limit : int, optional(default=len(G))
          Specify the maximum search depth
  
      sort_neighbors : function
          A function that takes the list of neighbors of given node as input, and
          returns an *iterator* over these neighbors but with custom ordering.
  
      Returns
      -------
      pred: iterator
          (node, predecessor) iterator where `predecessor` is the predecessor of
          `node` in a breadth first search starting from `source`.
  
      Examples
      --------
      >>> G = nx.path_graph(3)
      >>> dict(nx.bfs_predecessors(G, 0))
      {1: 0, 2: 1}
      >>> H = nx.Graph()
      >>> H.add_edges_from([(0, 1), (0, 2), (1, 3), (1, 4), (2, 5), (2, 6)])
      >>> dict(nx.bfs_predecessors(H, 0))
      {1: 0, 2: 0, 3: 1, 4: 1, 5: 2, 6: 2}
      >>> M = nx.Graph()
      >>> nx.add_path(M, [0, 1, 2, 3, 4, 5, 6])
      >>> nx.add_path(M, [2, 7, 8, 9, 10])
      >>> sorted(nx.bfs_predecessors(M, source=1, depth_limit=3))
      [(0, 1), (2, 1), (3, 2), (4, 3), (7, 2), (8, 7)]
      >>> N = nx.DiGraph()
      >>> nx.add_path(N, [0, 1, 2, 3, 4, 7])
      >>> nx.add_path(N, [3, 5, 6, 7])
      >>> sorted(nx.bfs_predecessors(N, source=2))
      [(3, 2), (4, 3), (5, 3), (6, 5), (7, 4)]
  
      Notes
      -----
      Based on http://www.ics.uci.edu/~eppstein/PADS/BFS.py
      by D. Eppstein, July 2004. The modifications
      to allow depth limits based on the Wikipedia article
      "`Depth-limited-search`_".
  
      .. _Depth-limited-search: https://en.wikipedia.org/wiki/Depth-limited_search
  
      See Also
      --------
      bfs_tree
      bfs_edges
      edge_bfs
      """
      for s, t in bfs_edges(
          G,
          source,
          depth_limit=depth_limit,
          sort_neighbors=sort_neighbors,
      ):
          yield (t, s)
  
file_path: networkx/networkx/algorithms/traversal/breadth_first_search.py
imports: import math
  from collections import deque
  import networkx
label_desc: Use image node_id 4 for calling a global function with example usage: bfs_predecessors(G, source, depth_limit, sort_neighbors) without return types